Method for receiving downlink signal, in wireless communication system supporting unlicensed band, and device for supporting same

ABSTRACT

Disclosed are a method for transmitting a downlink signal by a terminal from a base station, in a licensed assisted access (LAA) system for execution of listen-before-talk (LBT) based signal transmission by a base station or a terminal, and a device for supporting same. More particularly, even if the terminal does not receive from the base station information which indicates that from N−1th subframe to Nth subframe is a partial subframe (a subframe configuration in which a downlink signal is transmitted only on some of the symbols of a subframe), the terminal receives a physical downlink control channel (PDCCH) comprising uplink scheduling information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2017/000960, filed on Jan. 26, 2017, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application Nos. 62/287,889,filed on Jan. 27, 2016, 62/294,268, filed on Feb. 11, 2016, 62/314,979,filed on Mar. 29, 2016, and 62/319,272, filed on Apr. 6, 2016, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

Following description relates to a wireless communication systemsupporting an unlicensed band, and more particularly, to a method for aterminal to receive a downlink signal from a base station in a wirelesscommunication system supporting an unlicensed band and apparatusessupporting the same.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

DISCLOSURE OF THE INVENTION Technical Tasks

An object of the present invention is to provide a method for a UE toreceive a downlink signal from a base station when the base station orthe UE performs LBT (listen-before-talk) based signal transmission.

In particular, when a UE fails to receive information indicating that anN^(th) subframe corresponds to a partial subframe (a subframeconfiguration that a downlink signal is transmitted in a partial symbolonly of a subframe) in an N−1^(th) subframe, an object of the presentinvention is provide a method for the UE to efficiently receive adownlink signal from the base station.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The present invention provides a method for a terminal to receive adownlink signal from a base station in a wireless communication systemsupporting an unlicensed band and apparatuses supporting the same.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of receiving a downlink signal, which isreceived by a user equipment (UE) from a base station in a wirelesscommunication system supporting an unlicensed band, includes the stepsof, if a first PDCCH (physical downlink control channel) includinginformation indicating that a downlink signal is not transmitted in apartial symbol of an N^(th) subframe is not received in an N−1^(th)subframe (where, N is a natural number) and a second PDCCH includinginformation indicating that a downlink signal is not transmitted in apartial symbol of the N^(th) subframe is received in the N^(th)subframe, receiving a third PDCCH including uplink schedulinginformation in the N^(th) subframe.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, auser equipment receiving a downlink signal in a wireless communicationsystem supporting an unlicensed band includes a receiver, and aprocessor configured to operate in a manner of being connected with thereceiver, the processor, if a first PDCCH (physical downlink controlchannel) including information indicating that a downlink signal is nottransmitted in a partial symbol of an N^(th) subframe is not received inan N−1^(th) subframe (where, N is a natural number) and a second PDCCHincluding information indicating that a downlink signal is nottransmitted in a partial symbol of the N^(th) subframe is received inthe N^(th) subframe, configured to receive a third PDCCH containinguplink scheduling information in the N^(th) subframe.

In this case, the third PDCCH can be transmitted via a UE-specificsearch space.

In this case, the first PDCCH and the second PDCCH may correspond to acommon PDCCH.

And, the first PDCCH, the second PDCCH, and the third PDCCH can betransmitted via an unlicensed band.

And, the information indicating that the downlink signal is nottransmitted in the partial symbol of the N^(th) subframe can indicatethat the number of symbols occupied in the N^(th) subframe is less than14 symbols.

Technical solutions obtainable from the present invention arenon-limited the above-mentioned technical solutions. And, otherunmentioned technical solutions can be clearly understood from thefollowing description by those having ordinary skill in the technicalfield to which the present invention pertains.

Advantageous Effects

As is apparent from the above description, the embodiments of thepresent disclosure have the following effects.

According to the present invention, a base station can provide a ULgrant (or UL scheduling information) to a UE via a partial subframe(e.g., a downlink signal not including PDSCH) in a wireless accesssystem supporting an unlicensed band. In other word, when a base stationintends to transmit a UL grant (or UL scheduling information) to a UE,the base station can transmit the UL grant (or UL schedulinginformation) to the UE in a form of a partial subframe to minimizetransmission of unnecessary dummy signal.

In response to this, the UE can receive the UL grant (or UL schedulinginformation) via a partial subframe.

Hence, it is able to more efficiently allocate UL transmission between abase station and a UE in a wireless access system supporting anunlicensed band.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains. That is,effects which are not intended by the present invention may be derivedby those skilled in the art from the embodiments of the presentinvention.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, provide embodiments of the presentinvention together with detail explanation. Yet, a technicalcharacteristic of the present invention is not limited to a specificdrawing. Characteristics disclosed in each of the drawings are combinedwith each other to configure a new embodiment. Reference numerals ineach drawing correspond to structural elements.

FIG. 1 is a diagram illustrating physical channels and a signaltransmission method using the physical channels;

FIG. 2 is a diagram illustrating exemplary radio frame structures;

FIG. 3 is a diagram illustrating an exemplary resource grid for theduration of a downlink slot;

FIG. 4 is a diagram illustrating an exemplary structure of an uplinksubframe;

FIG. 5 is a diagram illustrating an exemplary structure of a downlinksubframe;

FIG. 6 is a diagram illustrating an exemplary CA environment supportedin an LTE-Unlicensed (LTE-U) system.

FIG. 7 is a diagram illustrating an exemplary Frame Based Equipment(FBE) operation as one of Listen-Before-Talk (LBT) operations;

FIG. 8 is a block diagram illustrating the FBE operation;

FIG. 9 is a diagram illustrating an exemplary Load Based Equipment (LBE)operation as one of the LBT operations;

FIG. 10 is a diagram for explaining methods of transmitting a DRSsupported in an LAA system;

FIG. 11 is a flowchart for explaining CAP and CWA;

FIG. 12 is a diagram illustrating a cross-carrier UL scheduling methodaccording to the present invention;

FIG. 13 is a diagram illustrating a UE behavior according to aself-carrier scheduling method in accordance with the present invention;

FIG. 14 is a diagram illustrating an operation of configuring HARQ-ACKtransmitted in an SF #n by ACK/NACK for 4 previous subframes startingfrom an SF #n−5;

FIG. 15 is a diagram illustrating a multi-channel LBT operation;

FIG. 16 is a diagram illustrating a method of defining MCOT proposed bythe present invention;

FIG. 17 is diagram illustrating configurations of a UE and a basestation in which proposed embodiments are implementable.

BEST MODE Mode for Invention

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentdisclosure (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmission end is a fixed and/or mobile node that provides a dataservice or a voice service and a reception end is a fixed and/or mobilenode that receives a data service or a voice service. Therefore, a UEmay serve as a transmission end and a BS may serve as a reception end,on an UpLink (UL). Likewise, the UE may serve as a reception end and theBS may serve as a transmission end, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

For example, the term, TxOP may be used interchangeably withtransmission period or Reserved Resource Period (RRP) in the same sense.Further, a Listen-Before-Talk (LBT) procedure may be performed for thesame purpose as a carrier sensing procedure for determining whether achannel state is idle or busy, CCA (Clear Channel Assessment), CAP(Channel Access Procedure).

Hereinafter, 3GPP LTE/LTE-A systems are explained, which are examples ofwireless access systems.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present disclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2(a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (Tf=307200·Ts) long, including equal-sized 20slots indexed from 0 to 19. Each slot is 0.5 ms (Tslot=15360·Ts) long.One subframe includes two successive slots. An ith subframe includes2ith and (2i+1)th slots. That is, a radio frame includes 10 subframes. Atime required for transmitting one subframe is defined as a TransmissionTime Interval (TTI). Ts is a sampling time given as Ts=1/(15kHz×2048)=3.2552×10−8 (about 33 ns). One slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or SC-FDMAsymbols in the time domain by a plurality of Resource Blocks (RBs) inthe frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(Tf=307200·Ts) long, including two half-frames each having a length of 5ms (=153600·Ts) long. Each half-frame includes five subframes each being1 ms (=30720·Ts) long. An ith subframe includes 2ith and (2i+1)th slotseach having a length of 0.5 ms (Tslot=15360·Ts). Ts is a sampling timegiven as Ts=1/(15 kHz×2048)=3.2552×10−8 (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink Special UpPTS UpPTS subframe Normal cyclic Extended cyclicNormal cyclic Extended cyclic configuration DwPTS prefix in uplinkprefix in uplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, NDLdepends on a DL transmission bandwidth. A structure of an uplink slotmay be identical to a structure of a downlink slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe is allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

2. LTE-U System

2.1 LTE-U System Configuration

Hereinafter, methods for transmitting and receiving data in a CAenvironment of an LTE-A band corresponding to a licensed band and anunlicensed band will be described. In the embodiments of the presentdisclosure, an LTE-U system means an LTE system that supports such a CAstatus of a licensed band and an unlicensed band. A WiFi band orBluetooth (BT) band may be used as the unlicensed band. LTE-A systemoperating on an unlicensed band is referred to as LAA (Licensed AssistedAccess) and the LAA may correspond to a scheme of performing datatransmission/reception in an unlicensed band using a combination with alicensed band.

FIG. 6 illustrates an example of a CA environment supported in an LTE-Usystem.

Hereinafter, for convenience of description, it is assumed that a UE isconfigured to perform wireless communication in each of a licensed bandand an unlicensed band by using two CCs. The methods which will bedescribed hereinafter may be applied to even a case where three or moreCCs are configured for a UE.

In the embodiments of the present disclosure, it is assumed that acarrier of the licensed band may be a primary CC (PCC or PCell), and acarrier of the unlicensed band may be a secondary CC (SCC or SCell).However, the embodiments of the present disclosure may be applied toeven a case where a plurality of licensed bands and a plurality ofunlicensed bands are used in a carrier aggregation method. Also, themethods suggested in the present disclosure may be applied to even a3GPP LTE system and another system.

In FIG. 6, one eNB supports both a licensed band and an unlicensed band.That is, the UE may transmit and receive control information and datathrough the PCC which is a licensed band, and may also transmit andreceive control information and data through the SCC which is anunlicensed band. However, the status shown in FIG. 6 is only example,and the embodiments of the present disclosure may be applied to even aCA environment that one UE accesses a plurality of eNBs.

For example, the UE may configure a macro eNB (M-eNB) and a PCell, andmay configure a small eNB (S-eNB) and an SCell. At this time, the macroeNB and the small eNB may be connected with each other through abackhaul network.

In the embodiments of the present disclosure, the unlicensed band may beoperated in a contention-based random access method. At this time, theeNB that supports the unlicensed band may perform a Carrier Sensing (CS)procedure prior to data transmission and reception. The CS proceduredetermines whether a corresponding band is reserved by another entity.

For example, the eNB of the SCell checks whether a current channel isbusy or idle. If it is determined that the corresponding band is idlestate, the eNB may transmit a scheduling grant to the UE to allocate aresource through (E)PDCCH of the PCell in case of a cross carrierscheduling mode and through PDCCH of the SCell in case of aself-scheduling mode, and may try data transmission and reception.

At this time, the eNB may configure a TxOP including N consecutivesubframes. In this case, a value of N and a use of the N subframes maypreviously be notified from the eNB to the UE through higher layersignaling through the PCell or through a physical control channel orphysical data channel.

2.2 Carrier Sensing (CS) Procedure

In embodiments of the present disclosure, a CS procedure may be called aClear Channel Assessment (CCA) procedure. In the CCA procedure, it maybe determined whether a channel is busy or idle based on a predeterminedCCA threshold or a CCA threshold configured by higher-layer signaling.For example, if energy higher than the CCA threshold is detected in anunlicensed band, SCell, it may be determined that the channel is busy oridle. If the channel is determined to be idle, an eNB may start signaltransmission in the SCell. This procedure may be referred to as LBT.

FIG. 7 is a view illustrating an exemplary Frame Based Equipment (FBE)operation as one of LBT operations.

The European Telecommunication Standards Institute (ETSI) regulation (EN301 893 V1.7.1) defines two LBT operations, Frame Based Equipment (FBE)and Load Based Equipment (LBE). In FBE, one fixed frame is comprised ofa channel occupancy time (e.g., 1 to 10 ms) being a time period duringwhich a communication node succeeding in channel access may continuetransmission, and an idle period being at least 5% of the channeloccupancy time, and CCA is defined as an operation for monitoring achannel during a CCA slot (at least 20 μs) at the end of the idleperiod.

A communication node periodically performs CCA on a per-fixed framebasis. If the channel is unoccupied, the communication node transmitsdata during the channel occupancy time. On the contrary, if the channelis occupied, the communication node defers the transmission and waitsuntil the CCA slot of the next period.

FIG. 8 is a block diagram illustrating the FBE operation.

Referring to FIG. 8, a communication node (i.e., eNB) managing an SCellperforms CCA during a CCA slot. If the channel is idle, thecommunication node performs data transmission (Tx). If the channel isbusy, the communication node waits for a time period calculated bysubtracting the CCA slot from a fixed frame period, and then resumesCCA.

The communication node transmits data during the channel occupancy time.Upon completion of the data transmission, the communication node waitsfor a time period calculated by subtracting the CCA slot from the idleperiod, and then resumes CCA. If the channel is idle but thecommunication node has no transmission data, the communication nodewaits for the time period calculated by subtracting the CCA slot fromthe fixed frame period, and then resumes CCA.

FIG. 9 is a view illustrating an exemplary LBE operation as one of theLBT operations.

Referring to FIG. 9(a), in LBE, the communication node first sets q(q∈{4, 5, . . . , 32}) and then performs CCA during one CCA slot.

FIG. 9(b) is a block diagram illustrating the LBE operation. The LBEoperation will be described with reference to FIG. 9(b).

The communication node may perform CCA during a CCA slot. If the channelis unoccupied in a first CCA slot, the communication node may transmitdata by securing a time period of up to (13/32)q ms.

On the contrary, if the channel is occupied in the first CCA slot, thecommunication node selects N (N∈{1, 2, . . . , q}) arbitrarily (i.e.,randomly) and stores the selected N value as an initial count. Then, thecommunication node senses a channel state on a CCA slot basis. Each timethe channel is unoccupied in one specific CCA slot, the communicationnode decrements the count by 1. If the count is 0, the communicationnode may transmit data by securing a time period of up to (13/32)q ms.

2.3 Discontinuous Transmission in DL

When discontinuous transmission is performed on an unlicensed carrierhaving a limited maximum transmission period, the discontinuoustransmission may influence on several functions necessary for performingan operation of LTE system. The several functions can be supported byone or more signals transmitted at a starting part of discontinuous LAADL transmission. The functions supported by the signals include such afunction as AGC configuration, channel reservation, and the like.

When a signal is transmitted by an LAA node, channel reservation has ameaning of transmitting signals via channels, which are occupied totransmit a signal to other nodes, after channel access is performed viaa successful LBT operation.

The functions, which are supported by one or more signals necessary forperforming an LAA operation including discontinuous DL transmission,include a function for detecting LAA DL transmission transmitted by a UEand a function for synchronizing frequency and time. In this case, therequirement of the functions does not mean that other availablefunctions are excluded. The functions can be supported by other methods.

2.3.1 Time and Frequency Synchronization

A design target recommended by LAA system is to support a UE to make theUE obtain time and frequency synchronization via a discovery signal formeasuring RRM (radio resource management) and each of reference signalsincluded in DL transmission bursts, or a combination thereof. Thediscovery signal for measuring RRM transmitted from a serving cell canbe used for obtaining coarse time or frequency synchronization.

2.3.2 DL Transmission Timing

When a DL LAA is designed, it may follow a CA timing relation betweenserving cells combined by CA, which is defined in LTE-A system (Rel-12or earlier), for subframe boundary adjustment. Yet, it does not meanthat a base station starts DL transmission only at a subframe boundary.Although all OFDM symbols are unavailable in a subframe, LAA system cansupport PDSCH transmission according to a result of an LBT operation. Inthis case, it is required to support transmission of control informationnecessary for performing the PDSCH transmission.

2.4 Measuring and Reporting RRM

LTE-A system can transmit a discovery signal at a start point forsupporting RRM functions including a function for detecting a cell. Inthis case, the discovery signal can be referred to as a discoveryreference signal (DRS). In order to support the RRM functions for LAA,the discovery signal of the LTE-A system and transmission/receptionfunctions of the discovery signal can be applied in a manner of beingchanged.

2.4.1 Discovery Reference Signal (DRS)

A DRS of LTE-A system is designed to support on/off operations of asmall cell. In this case, off small cells correspond to a state thatmost of functions are turned off except a periodic transmission of aDRS. DRSs are transmitted at a DRS transmission occasion with a periodof 40, 80, or 160 ms. A DMTC (discovery measurement timingconfiguration) corresponds to a time period capable of anticipating aDRS received by a UE. The DRS transmission occasion may occur at anypoint in the DMTC. A UE can anticipate that a DRS is continuouslytransmitted from a cell allocated to the UE with a correspondinginterval.

If a DRS of LTE-A system is used in LAA system, it may bring newconstraints. For example, although transmission of a DRS such as a veryshort control transmission without LBT can be permitted in severalregions, a short control transmission without LBT is not permitted inother several regions. Hence, a DRS transmission in the LAA system maybecome a target of LBT.

When a DRS is transmitted, if LBT is applied to the DRS, similar to aDRS transmitted in LTE-A system, the DRS may not be transmitted by aperiodic scheme. In particular, it may consider two schemes described inthe following to transmit a DRS in the LAA system.

As a first scheme, a DRS is transmitted at a fixed position only in aDMTC configured on the basis of a condition of LBT.

As a second scheme, a DRS transmission is permitted at one or moredifferent time positions in a DMTC configured on the basis of acondition of LBT.

As a different aspect of the second scheme, the number of time positionscan be restricted to one time position in a subframe. If it is moreprofitable, DRS transmission can be permitted at the outside of aconfigured DMTC as well as DRS transmission performed in the DMTC.

FIG. 10 is a diagram for explaining DRS transmission methods supportedby LAA system.

Referring to FIG. 10, the upper part of FIG. 10 shows the aforementionedfirst scheme for transmitting a DRS and the bottom part of FIG. 10 showsthe aforementioned second scheme for transmitting a DRS. In particular,in case of the first scheme, a UE can receive a DRS at a positiondetermined in a DMTC period only. On the contrary, in case of the secondscheme, a UE can receive a DRS at a random position in a DMTC period.

In LTE-A system, when a UE performs RRM measurement based on DRStransmission, the UE can perform single RRM measurement based on aplurality of DRS occasions. In case of using a DRS in LAA system, due tothe constraint of LBT, it is difficult to guarantee that the DRS istransmitted at a specific position. Even though a DRS is not actuallytransmitted from a base station, if a UE assumes that the DRS exists,quality of an RRM measurement result reported by the UE can bedeteriorated. Hence, when LAA DRS is designed, it is necessary to permitthe existence of a DRS to be detected in a single DRS occasion. By doingso, it may be able to make the UE combine the existence of the DRS withRRM measurement, which is performed on successfully detected DRSoccasions only.

Signals including a DRS do not guarantee DRS transmissions adjacent intime. In particular, if there is no data transmission in subframesaccompanied with a DRS, there may exist OFDM symbols in which a physicalsignal is not transmitted. While operating in an unlicensed band, othernodes may sense that a corresponding channel is in an idle state duringa silence period between DRS transmissions. In order to avoid theabovementioned problem, it is preferable that transmission burstsincluding a DRS signal are configured by adjacent OFDM symbols in whichseveral signals are transmitted.

2.5 Channel Access Procedure and Contention Window Adjustment Procedure

In the following, the aforementioned channel access procedure and thecontention window adjustment procedure are explained in the aspect of atransmission node.

FIG. 11 is a flowchart for explaining CAP and CWA.

In order for an LTE transmission node (e.g., a base station) to operatein LAA Scell(s) corresponding to an unlicensed band cell for DLtransmission, it may initiate a channel access procedure (CAP) [S1110].

The base station can randomly select a back-off counter N from acontention window (CW). In this case, the N is configured by an initialvalue Ninit [S1120]. The Ninit is randomly selected from among valuesranging from 0 to CW_(p).

Subsequently, if the back-off counter value (N) corresponds to 0[S1122], the base station terminates the CAP and performs Tx bursttransmission including PSCH [S1124]. On the contrary, if the back-offvalue is not 0, the base station reduces the back-off counter value by 1[S1130].

The base station checks whether or not a channel of the LAA Scell(s) isin an idle state [S1140]. If the channel is in the idle state, the basestation checks whether or not the back-off value corresponds to 0[S1150]. The base station repeatedly checks whether or not the channelis in the idle state until the back-off value becomes 0 while reducingthe back-off counter value by 1.

In the step S1140, if the channel is not in the idle state i.e., if thechannel is in a busy state, the base station checks whether or not thechannel is in the idle state during a defer duration (more than 15 usec)longer than a slot duration (e.g., 9 usec) [S1142]. If the channel is inthe idle state during the defer duration, the base station can resumethe CAP [S1144]. For example, when the back-off counter value Ninitcorresponds to 10, if the channel state is determined as busy after theback-off counter value is reduced to 5, the base station senses thechannel during the defer duration and determines whether or not thechannel is in the idle state. In this case, if the channel is in theidle state during the defer duration, the base station performs the CAPagain from the back-off counter value 5 (or, from the back-off countervalue 4 by reducing the value by 1) rather than configures the back-offcounter value Ninit. On the contrary, if the channel is in the busystate during the defer duration, the base station performs the stepS1142 again to check whether or not the channel is in the idle stateduring a new defer duration.

Referring back to FIG. 11, the base station checks whether or not theback-off counter value (N) becomes 0 [S1150]. If the back-off countervalue (N) becomes 0, the base station terminates the CAP and may be ableto transmit a Tx burst including PDSCH.

The base station can receive HARQ-ACK information from a UE in responseto the Tx burst [S1170]. The base station can adjust a CWS (contentionwindow size) based on the HARQ-ACK information received from the UE[S1180].

In the step S1180, as a method of adjusting the CWS, the base stationcan adjust the CWS based on HARQ-ACK information on a first subframe ofa most recently transmitted Tx burst (i.e., a start subframe of the Txburst).

In this case, the base station can set an initial CW to each priorityclass before the CWP is performed. Subsequently, if a probability thatHARQ-ACK values corresponding to PDSCH transmitted in a referencesubframe are determined as NACK is equal to or greater than 80%, thebase station increases CW values set to each priority class to a nexthigher priority.

In the step S1160, PDSCH can be assigned by a self-carrier schedulingscheme or a cross-carrier scheduling scheme. If the PDSCH is assigned bythe self-carrier scheduling scheme, the base station counts DTX,NACK/DTX, or ANY state among the HARQ-ACK information fed back by the UEas NACK. If the PDSCH is assigned by the cross-carrier schedulingscheme, the base station counts the NACK/DTX and the ANY states as NACKand does not count the DTX state as NACK among the HARQ-ACK informationfed back by the UE.

If bundling is performed over M (M>=2) number of subframes and bundledHARQ-ACK information is received, the base station may consider thebundled HARQ-ACK information as M number of HARQ-ACK responses. In thiscase, it is preferable that a reference subframe is included in the Mnumber of bundled subframes.

3. Proposed Embodiment

When a base station or a UE performs LBT (listen-before-talk)-basedsignal transmission in a wireless communication system consisting of thebase station and the UE, the present invention proposes a method ofperforming DL transmission and configurations applicable to the method.

According to the present invention, a base station or a UE shouldperform LBT to transmit a signal on an unlicensed band. When the basestation or the UE transmits a signal, it is necessary to make signalinterference not to be occurred with different communication nodes suchas Wi-Fi, and the like. For example, according to Wi-Fi standard, a CCAthreshold value is regulated by −62 dBm and −82 dBm for a non-Wi-Fisignal and a Wi-Fi signal, respectively. In particular, if an STA(station) or an AP (access point) senses a signal received with power(or energy) equal to or greater than −62 dBm rather than Wi-Fi, the STAor the AP does not perform signal transmission.

In this case, it may be difficult to always guarantee DL transmission ofan eNB or UL transmission of a UE on an unlicensed band. Hence, a UEoperating on the unlicensed band may maintain access with a differentcell operating on a licensed band to stably control mobility, RRM (radioresource management) function, and the like. In the present invention,for clarity, a cell accessed by a UE on an unlicensed band is referredto as an UScell (or, LAA Scell) and a cell accessed by the UE on alicensed band is referred to as a Pcell. In particular, a scheme ofperforming data transmission/reception on the unlicensed band using acombination with the licensed band is generally called LAA (licensedassisted access).

TABLE 2 Channel Access Priority allowed Class (p) m_(p) CW_(min, p)CW_(max, p) T_(mcot, p) CW_(p) sizes 1 1 3 7 2 ms {3, 7}  2 1 7 15 3 ms{7, 15} 3 3 15 63 8 or 10 ms {15, 31, 63} 4 7 15 1023 8 or 10 ms {15,31, 63, 127, 255, 511, 1023}

As shown in Table 2, in Rel-13 LAA system, 4 channel access priorityclasses are defined in total. And, a length of a defer period, a CWS,MCOT (maximum channel occupancy time), and the like are definedaccording to each of the channel access priority classes. Hence, when aneNB transmits a downlink signal via an unlicensed band, the eNB performsrandom backoff by utilizing LBT parameters determined according to achannel access priority class and may be then able to access a channelduring limited maximum transmission time only after the random backoffis completed.

For example, in case of the channel access priority class 1/2/3/4, themaximum channel occupancy time (MCOT) is determined by 2/3/8/8 ms. Themaximum channel occupancy time (MCOT) is determined by 2/3/10/10 ms inenvironment where other RAT such as Wi-Fi does not exists (e.g., bylevel of regulation).

As shown in Table 2, a set of CWSs capable of being configured accordingto a class is defined. One of points different from Wi-Fi system is inthat a different backoff counter value is not defined according to achannel access priority class and LBT is performed using a singlebackoff counter value (this is referred to as single engine LBT).

For example, when an eNB intends to access a channel via an LBToperation of a channel access priority class 3, since CWmin (=15) isconfigured as an initial CWS, the eNB performs random backoff byrandomly selecting an integer from among numbers ranging from 0 to 15.If a backoff counter value becomes 0, the eNB starts DL Tx and randomlyselects a new backoff counter for a next DL Tx burst after the DL Txburst is completed. In this case, if an event for increasing a CWS istriggered, the eNB increases a size of the CWS to 31 corresponding to anext size, randomly selects an integer from among numbers ranging from 0to 31, and performs random backoff.

In this case, when a CWS of the class 3 is increased, CWSs of allclasses are increased as well. In particular, if the CW of the class 3becomes 31, a CWS of a class 1/2/4 becomes 7/15/31. If an event fordecreasing a CWS is triggered, CWS values of all classes are initializedby CWmin irrespective of a CWS value of the triggering timing.

The present invention intends to propose DL transmission methods in LAAsystem based on the abovementioned contents. Specifically, the presentinvention proposes a condition for transmitting a UL grant whencross-carrier scheduling from L-cell accompanied with an LBT procedureis performed in LAA Scell, a method of transmitting a UL grant viaself-carrier scheduling, a method of defining a reference subframe foradjusting a contention window size (hereinafter, CWS), an operation ofadjusting a CWS for a method of performing category 4-based LBT on aspecific carrier only among a plurality of carriers, and the like.

3.1 Scheduling Method

Basically, UL transmission can be performed based on scheduling of aneNB in LAA Scell. In particular, the eNB transmits a UL grant (includingUL scheduling information) to a UE at the timing of SF #n. Havingreceived the UL scheduling information, the UE transmits UL data at thetiming of SF #n+k (e.g., k=4) via an allocated resource. In this case, ascheduling method can be classified into a self-carrier schedulingmethod and a cross-carrier scheduling method. According to theself-carrier scheduling method, a UL grant is transmitted in LAA Scellin which UL data is transmitted. According to the cross-carrierscheduling method, a UL grant is transmitted in an L-cell (rather thanLAA Scell).

3.1.1 Cross-Carrier UL Scheduling from L-Cell with LBT

When an eNB performs cross-carrier UL scheduling in an L-cell, twomethods are available.

(1) When an eNB transmits a UL grant in an L-cell, the eNB transmits theUL grant irrespective of a channel state of an LAA Scell and a scheduledUE attempts to transmit UL data after performing LBT for relatively longtime.

(2) When an eNB transmit a UL grant in an L-cell, the eNB transmits theUL grant only when a channel is determined as idle after LBT isperformed in an LAA Scell. A scheduled UE attempts to transmit UL dataafter performing LBT for relatively shorter time compared to the method(1).

In this case, according to the method (2), it is necessary not only foran eNB but also for a UE to successfully perform LBT to transmit ULdata. Hence, it may be able to configure the UE according to the method(2) to perform LBT for a shorter period of time compared to the UEaccording to the method (1). By doing so, a UL data transmissionprobability in the LAA Scell can be similarly adjusted between the twomethods.

FIG. 12 is a diagram illustrating a cross-carrier UL scheduling methodaccording to the present invention.

FIG. 12 illustrates cross-carrier UL scheduling to which theaforementioned method (2) is applied. In order to transmit a UL grant ina second subframe (SF #2) in an Lcell, an eNB performs LBT in an LAAScell. The eNB can attempt to transmit the UL grant from the SF #2 onlywhen the LBT is successfully completed immediately before the SF #2starts. If a UL resource scheduled in the SF #2 exists in an SF #6, aUE, which has received the UL grant, can perform LBT prior to the SF #6(or predetermined timing before and after a subframe boundary) toinitiate UL data transmission in the SF #6.

In this case, it is necessary to clearly define a success condition ofLBT for transmitting a UL grant transmitted by the eNB in the SF #2. Ifthe eNB successfully performs the LBT prior to a subframe boundary ofthe SF #2 to transmit the UL grant via self-carrier scheduling in theLAA Scell, the eNB can occupy a channel by transmitting a reservationsignal and the like in advance. On the contrary, when the eNB performsLBT in the LAA Scell to perform cross-carrier scheduling in the L-cell,if the eNB transmits a reservation signal based on the LBT which issuccessfully performed prior to the subframe boundary of the SF #2,since the reservation signal acts as interference only to other nodes,it may not be preferable. However, if the success of the LBT performedby the eNB is restricted to be completed at the timing immediatelybefore the SF #2, it may have a demerit in that a probability oftransmitting the UL grant transmitted by the eNB can be lowered comparedto the self-carrier scheduling. The present invention proposes an LBTsuccess condition for transmitting a UL grant via cross-carrierscheduling as follows in consideration of the abovementioned contents.

[First LBT success condition] If an eNB (or a UE scheduled by the eNB)is transmitting a signal in a subframe prior to a subframe in which a ULgrant is transmitted via cross-carrier scheduling in an LAA Scell, theeNB can transmit a UL grant without performing LBT in the LAA Scell. Forexample, in FIG. 12, if an eNB performs transmission in a first subframe(SF #1) (or during the last symbol of the SF #1) in LAA Scell, the eNBcan transmit a UL grant in an SF #2 without any additional LBT.

[Second LBT success condition] When an eNB performs LBT in LAA Scell totransmit a UL grant via cross-carrier scheduling, the eNB can transmitthe UL grant only when the LBT is completed at the timing of an SF startboundary at which the UL grant is to be transmitted. Or, the eNB cantransmit a UL grant only when LBT is completed at the timing of a secondslot boundary of a subframe immediately before a subframe in which theUL grant is to be transmitted.

In this case, it may be able to restrict the eNB to perform the LBT onlywhen a signal is not transmitted in the LAA Scell at the timing of asubframe immediately before a subframe in which a UL grant is to betransmitted via cross-carrier scheduling. For example, referring to FIG.12, if a signal is not transmitted in (at least of) the last symbol ofan SF #1, the eNB should perform LBT in the LAA Scell.

In this case, the LBT performed in the LAA Scell may correspond tocategory 4 based LBT or single CCA slot LBT. In case of the category 4based LBT, the eNB should complete the LBT at the timing of a subframestart boundary (or a second slot boundary of a subframe immediatelybefore a subframe in which the LBT is performed) using self-deferral andthe like. In case of the single CCA slot LBT, if the eNB determines thata channel is idle during X us (e.g., 25 us) from timing of a subframestart boundary (or a second slot boundary of a subframe immediatelybefore a subframe in which the LBT is performed), the eNB can completethe LBT.

When a UL grant is transmitted via cross-carrier scheduling, a type ofLBT performed in the LAA Scell can be specifically or separatelyconfigured. For example, in case of a cross-carrier UL scheduling grant,it may be able to predefine a rule that an eNB performs the single CCAslot LBT. Or, it may be able to define a rule that the eNB performs thecategory 4 based LBT using a specific CWS(s) (or LBT parameters of aspecific channel access priority class).

Or, a type of LBT performed in the LAA Scell can be determined accordingto a type of multi-channel LBT performed in the LAA Scell. For example,if all carriers of a group of carriers including the LAA Scell apply thecategory 4 based LBT, an eNB can perform the category 4 based LBT in theLAA Scell. As a different example, if the category 4 based LBT isapplied to a specific carrier only among the group of carriers includingthe LAA Scell, the eNB can perform configured LBT in the LAA Scell.

[Third LBT success condition] When an eNB performs LBT in LAA Scell totransmit a cross-carrier scheduling UL grant, if the LBT is completedwithin T us (or K symbols (K=3)) from the timing of a start boundary ofa subframe in which the UL grant is to be transmitted (or a second slotboundary of a subframe immediately before a subframe in which the ULgrant is to be transmitted), the eNB can transmit the UL grant. Forexample, when K corresponds to 2, if the LBT is completed within twosymbols prior to a start subframe boundary of SF #2 (or a second slotboundary of a subframe immediately before a subframe in which the ULgrant is to be transmitted), the eNB can transmit the UL grant.

In this case, it may be able to configure the eNB to perform LBT onlywhen an additional signal is not transmitted in the LAA Scell within Tus (or within K symbols) from the timing of a start boundary of asubframe prior to a subframe in which a cross-carrier scheduling ULgrant is transmitted.

In this case, the LBT performed in the LAA Scell may correspond tocategory 4 based LBT or single CCA slot LBT. When a UL grant istransmitted via cross-carrier scheduling, a type of LBT performed in theLAA Scell can be specifically or separately configured. For example, incase of a cross-carrier UL scheduling grant, it may be able to predefinea rule that an eNB performs the single CCA slot LBT. Or, it may be ableto define a rule that the eNB performs the category 4 based LBT using aspecific CWS(s) (or LBT parameters of a specific channel access priorityclass).

As a different example, a type of LBT performed in the LAA Scell can bedetermined according to a type of multi-channel LBT performed in the LAAScell. For example, if all carriers of a group of carriers including theLAA Scell apply the category 4 based LBT, an eNB can perform thecategory 4 based LBT in the LAA Scell. As a different example, if thecategory 4 based LBT is applied to a specific carrier only among thegroup of carriers including the LAA Scell, the eNB can performconfigured LBT in the LAA Scell.

In the aforementioned methods, an eNB performs LBT to transmit a ULgrant. In this case, the LBT may operate irrespective of LBT fortransmitting PDSCH or LBT for transmitting a DRS not including PDSCH.

In the aforementioned methods, if it fails to satisfy a successcondition of LBT for transmitting a cross-carrier scheduling grant, itmay be able to configure an eNB to apply [first LBT success condition]or fallback to the [first LBT success condition] to make a scheduled UEperform LBT for a relatively long time and then attempt to perform ULdata transmission. In this case, in order to make the scheduled UEperform the LBT for a relatively long time, the eNB can signal a biggerCWS value (or a backoff counter value selected based on the bigger CWSvalue) to the scheduled UE.

3.1.2 UL Grant Transmission Method Via Self-Carrier Scheduling

When an eNB intends to transmit a UL grant via self-scheduling withoutDL data to be transmitted in LAA Scell, the eNB can transmit acorresponding signal by configuring a partial subframe with (E)PDCCHonly without PDSCH by utilizing a DwPTS (downlink pilot time slot) of alength of at least 3 OFDM symbols. In this case, the eNB can perform LBTduring a timing gap between the partial subframe and a next subframe toincrease a probability of starting UL (or DL) transmission in the nextsubframe.

In LAA system to which the present invention is applied, it may be ableto configure a prescribed time period (i.e., a transmission gap) duringwhich signal transmission is not performed in a part of subframes toenable an eNB or a UE to transmit a signal in contiguous subframes. Inthis case, for clarity, a subframe to which a transmission gap is set isreferred to as a partial subframe. In particular, if a transmission gapis set to symbols located at the forepart of a specific subframe in timedomain, it is referred to as a start partial subframe (or initialpartial subframe). If a transmission gap is set to symbols located atthe latter part of a specific subframe in time domain, it is referred toas an end partial subframe.

However, in the LAA system to which the present invention is applied, ifan eNB transmits a signal in an end partial subframe (a subframe ofwhich the last partial symbol is emptied out) only, a UE is unable tointactly (perfectly) receive the subframe or a signal transmitted in thesubframe. Specifically, when an SF #n corresponds to an end partialsubframe, if a UE fails to receive information indicating that a nextsubframe corresponds to a partial subframe in an SF #n−1 from an eNB,the UE may not attempt to receive a signal transmitted in the SF #ncorresponding to the end partial subframe.

This is because a transmission point of a CRS (cell-specific referencesignal)/DMRS (demodulation references signal) transmitted in a partialsubframe is different from a transmission point of a CRS/DMRStransmitted in a full subframe (a subframe to which a transmission gapis not set). In particular, this is because, since a channel estimationmethod and a data processing method are different, it is necessary for aUE to have time for preparing the methods. In other word, in order foran eNB to properly transmit a self-scheduling UL grant to a UE withoutPDSCH, the eNB should transmit a signal using a full subframe of 1 ms.In the present invention, self-carrier scheduling methods appropriatefor the situation above are proposed.

3.1.2.1 First Self-Carrier Scheduling Method

Although an eNB transmits a signal to a UE using an end partial subframein an SF #n, the UE can be configured to mandatorily receive PDCCH. Anoperation described in the following is explained with reference to FIG.13.

FIG. 13 is a diagram illustrating a UE behavior according to aself-carrier scheduling method in accordance with the present invention.As shown in FIG. 13, an eNB may not transmit information indicating thata next subframe (i.e., SF #n) corresponds to a partial subframe to a UEin an SF #n−1. Or, although the eNB transmits the information to the UE,the UE may fail to receive the information due to various reasons. Theinformation can be transmitted using DCI (downlink control information).In this case, the present invention proposes a method of configuring theUE to receive PDCCH transmitted in the SF #n all the time.

As a different example, although an eNB transmits a signal to a UE usingan initial partial subframe (a subframe of which a first partial symbolis emptied out) in an SF #n−1, the UE can be configured to receive PDCCHtransmitted in an SF #n all the time.

In addition, a UE receives PDCCH transmitted from a common search spaceto identify the number of OFDM symbols constructing the SF #n.Additionally, the UE can also receive PDCCH (i.e., UL scheduling DCI)existing in a UE-specific search space.

Specifically, as shown in FIG. 13, according to the present invention, aUE is unable to receive PDCCH (or DCI) in an SF #n−1. The UE is able toreceive PDCCH (or DCI) in an SF #n. In this case, when the UE is unableto receive the PDCCH (or DCI) in the SF #n−1, it includes not only acase that an eNB does not transmit PDCCH (or DCI) in the SF #n−1 butalso a case that the UE is unable to receive the PDCCH (or DCI)transmitted by the eNB in the SF #n−1. In this case, the PDCCH caninclude information indicating that the SF #n corresponds to a partialsubframe (a subframe that a DL signal is not transmitted in a part ofsymbols, e.g., a subframe of which the number of occupied symbols isless than 14).

In this case, according to the present invention, the UE can receivePDCCH including UL scheduling information transmitted in the SF #n. And,the UE can receive information indicating that the SF #n corresponds toa partial subframe in the SF #n. In this case, the UE can receive thePDCCHs on an unlicensed band (LAA Scell).

According to the configuration above, an eNB can also provide a UL grant(or UL scheduling information) to a UE via a partial subframe (e.g., DLsignal not including PDSCH). In other word, when the eNB intends totransmit the UL grant (or UL scheduling information) to the UE, the eNBcan transmit the UL grant (or UL scheduling information) to the UE in aform of a partial subframe to minimize transmission of unnecessary dummysignal.

3.1.2.2 Second Self-Carrier Scheduling Method

The aforementioned first self-carrier scheduling method has a limit inthat the method is applied to a UE scheduled via PDCCH only. Forexample, when a UE receives EPDCCH (enhanced PDCCH), if informationindicating that an SF #n corresponds to an end partial subframe does notexist in an SF #n−1 or if the UE knows that the SF #n corresponds to anend partial subframe while failing to receive the information, since itis difficult for the UE to know a DMRS pattern in the SF #n, it isdifficult for the UE to successfully receive EPDCCH in the SF #ncorresponding to the end partial subframe.

As a method, it is able to transmit a subframe using a full subframe.However, it is unable to prepare a timing gap for performing LBT of aneNB or a UE. In order to supplement this, a UE can be configured tomonitor PDCCH rather than EPDCCH in an end partial subframe. Forexample, if a common search space PDCCH or PHICH indicates that asubframe corresponds to a PDCCH monitoring subframe, although a UE isscheduled by EPDCCH, the UE can be configured to receive scheduling DCIvia PDCCH rather than EPDCCH in the subframe.

Or, in order for a UE to receive EPDCCH, it is necessary for the UE toknow a DMRS pattern. Hence, it may be able to apply a method describedin the following to receive EPDCCH in an SF #n corresponding to an endpartial subframe.

More specifically, as mentioned earlier in the first self-carrierscheduling method, if the UE becomes aware that the SF #n corresponds tothe end partial subframe (via common PDCCH) in the SF #n−1 without theinformation indicating that the SF #n corresponds to the end partialsubframe, a UE behavior can be configured to receive EPDCCH (i.e., ULscheduling DCI) in the SF #n. This is because, in order to decode EPDCCHcodeword having a size considerably smaller than a size of PDSCH,although EPDCCH is decoded using a DMRS pattern which is checked bydecoding a common PDCCH of a corresponding subframe, it is able toperform UE implementation without any serious problem.

3.1.2.3 Third Self-Carrier Scheduling Method

In order to minimize a transmission count of a subframe configured by aUL grant only without PDSCH, it may allow cross-carrier scheduling to beperformed on a different LAA Scell in an LAA Scell or allowmulti-carrier scheduling to be performed on a plurality of LAA Scells inan LAA Scell.

It may not allow the aforementioned various self-carrier UL schedulingmethods to be performed on an initial partial subframe. In other word, aUE may not expect to receive a UL grant in an initial partial subframe.For more specific explanation, when a UE receives a UL grant in an SF #nvia PDCCH, assume that it takes time as much as k ms for the UE toprocess a series of procedures such as PDCCH processing, timing advance,UL data (e.g., PUSCH/PUCCH/SRS) mapping, and the like. When the UEreceives the UL grant via PDCCH of an initial partial subframe of the SF#n, if the UE still transmits UL data in an SF #n+k, the PDCCH of theinitial partial subframe of the SF #n is transmitted via OFDM symbolindexes 7 to 9 rather than OFDM symbol indexes 0 to 2, the UE requiresless time as much as 0.5 ms compared to a legacy operation. For thisreason, it may not allow self-carrier UL scheduling to be performed inan initial partial subframe in consideration of implementationcomplexity of the UE.

Or, although self-carrier UL scheduling of an initial partial subframeis allowed, a UL grant to PUSCH/PUCCH/SRS transmission delay value canbe differently configured depending on whether or not a specificsubframe corresponds to a initial partial subframe. For example, if a UEreceives a UL grant via PDCCH of an SF #n rather than an initial partialsubframe, the UE transmits UL data in an SF #n+k. On the contrary, if aUE receive s UL grant via PDCCH of an SF #n corresponding to an initialpartial subframe, the UE can be configured to transmit UL data in an SF#n+k+m (m>0). In this case, a value of the m can be differentlyconfigured depending on whether a path on which a UL grant istransmitted corresponds to PDCCH or EPDCCH. For example, if the UL grantis transmitted via EPDCCH, the value of the m is set to 0. If the ULgrant is transmitted via EPDCCH, the value of the m can be set to 1.

3.2 LBT Method

3.2.1 Method of Defining Reference Subframe for Adjusting CWS

Basically, CWS adjustment relates to ACK/NACK ratio of DL data. A DLsubframe considering HARQ-ACK feedback is defined as a referencesubframe for adjusting a CWS. In Rel-13 LAA system, event triggering,which triggers the increase or the decrease of a CWS value, relates toACK/NACK information of a very first subframe of a DL Tx burst. If morethan 80% of HARQ-ACK values of a very first subframe of a recent DL Txburst are NACK, a CWS is increased. Otherwise, the CWS is reset. In thiscase, if the first subframe of the DL Tx burst corresponds to an initialpartial subframe, it may consider not only ACK/NACK information of thefirst subframe but also ACK/NACK information of a full subframeappearing immediately after the first subframe.

In Rel-13 LAA system, a reference subframe is defined as follows.

A reference subframe k is the starting subframe of the most recenttransmission on the channel made by the eNB, for which HARQ-ACK feedbackis available.

In this case, it is necessary to clearly define the meaning of the‘HARQ-ACK feedback is available’ in consideration of the following case.

-   -   Among the most recent DL Tx burst, when PDSCH transmitted in a        first SF #n is different from a PUCCH cell of a UE #2, it may be        able to configure a UE #1 to feedback HARQ-ACK at the timing of        SF #n+k and configure the UE #2 to feedback HARQ-ACK at the        timing of SF #n+k+j. In this case, if an eNB intends to update        an LBT parameter between the timing of SF #n+k and the timing of        SF #n+k+j, it is not clear whether the eNB or the UE is able to        consider the SF #n capable of using a partial HARQ-ACK feedback        (i.e., HARQ-ACK feedback of the UE #1) only as a reference        subframe.

A first subframe (SF #n) of the most recent DL Tx burst may correspondto a partial subframe and HARQ-ACK feedback on the SF #n can be receivedin the SF #n+k. In this case, when the eNB intends to update an LBTparameter at the timing of the SF #n+k, the timing of the SF #n+k maycorrespond to timing at which HARQ-ACK feedback on a second subframe (SF#n+1) of the recent DL Tx burst is not received yet. In this case, it isnot clear whether or not the eNB or the UE is able to consider the SF #nand the SF #n+1 as a reference subframe.

In order to solve the ambiguity, the present invention proposes a methodof clearly defining a reference subframe as follows.

(1) A subframe can be considered as a reference subframe only when allHARQ-ACK feedbacks are available.

(2) If HARQ-ACK feedback is partly usable, a corresponding subframe isconsidered as a reference subframe and unusable (non-available) HARQ-ACKfeedback may not be utilized for adjusting a CWS.

In addition, it is able to allow HARQ-ACK on a PDSCH to be transmittedin at least one subframe among a plurality of subframes in preparationfor a case that HARQ-ACK transmission is introduced on an unlicensedband (U-cell) and HARQ-ACK transmission is not attempted due to thefailure of LBT. In this case, it may be necessary to define availableHARQ-ACK feedback again.

In this case, HARQ-ACK can be transmitted via PUCCH or can betransmitted in a manner of being piggybacked via PUSCH. For example,HARQ-ACK to be transmitted in an SF #n can be configured by ACK/NACKinformation on the L number of subframes appearing prior to an SF #n−k.(k and L can be determined in advance or can be configured via physicallayer signaling or higher layer signaling). As a different example,HARQ-ACK to be transmitted in the SF #n can be configured by a pluralityof HARQ process numbers or HARQ-ACK according to a DAI (downlinkassignment index).

FIG. 14 is a diagram illustrating an operation of configuring HARQ-ACKtransmitted in an SF #n by ACK/NACK for 4 previous subframes startingfrom an SF #n−5.

As shown in FIG. 14, if an eNB starts to transmit a DL TX burst from anSF #2, HARQ-ACK feedback for a reference subframe of the DL Tx burst canbe received in subframes ranging from an SF #7 to an SF #10. In thiscase, whether or not HARQ-ACK is available is determined by an eNB inevery subframe from the SF #7 to the SF #10. If HARQ-ACK feedback on theSF #2 is detected in a subframe from among the 4 subframes, it is ableto define that HARQ-ACK for the SF #2 is available at the timing of thesubframe. If HARQ-ACK feedback is not detected until the SF #10, the eNBmay consider that a UE did not transmit HARQ-ACK or the eNB has failedto detect HARQ-ACK feedback.

3.2.2 Method of Adjusting CWS in Multi-Channel LBT

In Rel-13 LAA system, a multi-channel LBT method is mainly classifiedinto two types. One is to perform category 4 based LBT in all channelsbelonging to a group carrier (type A) and another is to perform category4 based LBT in a single channel only among channels belonging to a groupcarrier (type B). In this case, when the type B multi-channel LBT isperformed, a representative carrier on which the category 4 based LBT isperformed can be randomly changed in every DL Tx burst or can be changedwith a period of 1 second.

FIG. 15 is a diagram illustrating a multi-channel LBT operation.

In FIG. 15, assume that CCs #1 to #3 correspond to a group carrier. Inthis case, the CC #2 can be configured as a carrier on which category 4based LBT is performed. In particular, whether or not a channel is idleon the CC #1 and the CC #3 during 25 us is determined on the basis ofthe timing at which the LBT ends on the CC #2. If it is determined as achannel is idle on the CC #1 only, an eNB attempts to simultaneouslytransmit a signal on the CC #1 and the CC #2 only and the eNB does notattempt DL transmission on the CC #3.

In FIG. 15, like the timing of SF #7, when DL Tx burst ends and abackoff counter is randomly selected, an eNB or a UE should update anLBT parameter value (e.g., CWS). In this case, as a method of updatingthe LBT parameter value, it is able to determine whether or not a CWS isadjusted using a reference subframe on all carriers and adjust CWSs ofall priority classes of a carrier on which category 4 based LBT isperformed. In particular, in FIG. 15, an eNB can adjust a CWS based onACK/NACK ratio of HARQ-ACK feedback corresponding to PDSCH transmittedon the CC #1 and the CC #2 at the timing of SF #3. When the eNBincreases or decreases a CWS based on LBT parameter update, the eNBincrease or decreases CWSs of all priority classes of the CC #2 (or a CCon which newly selected category 4 based LBT is to be performed).

However, since a CC on which category 4 based LBT is to be performed ischanged in every DL Tx burst, it may not be preferable to update a CWSof a specific CC only. Hence, whether to adjust a CWS is determinedusing a reference subframe on all carriers, the present inventionproposes a method of adjusting not only a CWS of a carrier on whichcategory 4 LBT is performed but also a CWS of all priority classes ofall carriers belonging to a carrier group. For example, when an LBTparameter is updated at the timing of SF #7, an eNB or a UE can adjust aCWS value of all carriers. This operation can be restrictively appliedto a case that an eNB changes a representative carrier on which category4 based LBT is performed in every DL Tx burst.

3.2.3 Method of Performing LBT when MCOT is Restricted by Regulation

In Rel-13 LAA system, as shown in Table 1, total 4 channel accesspriority classes exist and a length of a defer period, a CWS (contentionwindow size), MCOT (maximum channel occupancy time) and the like aredetermined according to each class. In particular, an eNB performsrandom backoff using determined parameters according to a channel accesspriority class and there is a limit on maximum transmission time forwhich a signal is transmitted by accessing a channel after the randombackoff is completed. In this case, if MCOT longer than time permittedby regulation (e.g., regulation of Japan) is applied, an eNB can beconfigured to additionally perform CCA during predetermined time (e.g.,34 us) after the time permitted by the regulation.

TABLE 3 For LAA operation in Japan, if the eNB has transmitted atransmission after N = 0 in step 4 of the procedure above, the eNB maytransmit the next continuous transmission, for duration of maximum T_(j)= 4 msec, immediately after sensing the channel for at least a sensinginterval of T_(js) = 34 usec, if the power detected by the eNB duringT_(js) is less than X_(Thresh), and if the total sensing andtransmission time is not more than 1000 · T_(mcot) + └T_(mcot)/T_(j)┘ ·T_(js) μsec.

For example, according to the regulation of Japan, if a transmissionentity is not permitted to continuously perform transmission more than 4ms (=T_j) on an unlicensed band, the transmission entity performs CCAduring at least 34 us. If it is determined as a channel is idle, thetransmission entity can resume transmission. In order for thetransmission entity to continuously transmit a signal during 5 ms(=T_mcot), the transmission entity performs transmission during 4 ms,performs CCA during 34 us (=T_js), and transmits the remaining 1 ms. Inorder for the transmission entity to continuously transmit a signalduring 10 ms (=T_mcot), the transmission entity performs transmissionduring first 4 ms, performs CCA during at least 34 us (=T_js), performstransmission during second 4 ms, performs CCA during at least 34 us(=T_js), and transmits the remaining 2 ms. In particular, as shown inthe last sentence of Table 3, the operation above can be permittedduring time described in the following equation 1 only.1000·T _(mcot) +└T _(mcot) /T _(j) ┘·T _(js) usec  [Equation 1]

For example, if T_mcot corresponds to 4 ms, time as much as 4 ms(transmission time)+34 us (CCA) is permitted to an eNB according to theequation 1. However, if T_mcot corresponds to 4 ms, since it is able toperform transmission using a single DL Tx burst, it is preferable forthe eNB to end signal transmission without CCA.

As a different example, if T_mcot corresponds to 8 ms, time as much as 8ms (transmission time)+2*34 us (CCA) is permitted to an eNB according tothe equation 1. However, if T_mcot corresponds to 8 ms, since it is ableto perform transmission using two DL Tx bursts, it is preferable for theeNB to perform CCA one time only. In particular, according to theequation 1, if T_mcot becomes a multiple of T_j, CCA is unnecessarilyperformed one more time. In order to solve the problem, the presentinvention proposes equations 2 to 6 instead of the equation 1.1000·T _(mcot)+└(T _(mcot) −A)/T _(j) ┘·T _(js) u sec  [Equation 2]

In this case, A should be a value equal to or less than 1 ms. Forexample, the A may correspond to 1 ms.1000·T _(mcot) +└T _(mcot) /T _(j) −A┘·T _(js) u sec  [Equation 3]

In this case, A may correspond to 0.1 ms.1000·T _(mcot)+ceiling((T _(mcot) −A)/T _(j))·T _(js) u sec  [Equation4]

In this case, A should be a value equal to or greater than T_j. Forexample, the A may correspond to T_j.1000·T _(mcot)+ceiling(T _(mcot) /T _(j) −A)·T _(js) u sec  [Equation 5]

In this case, A may correspond to 1 ms.

$\quad\begin{matrix}\left\{ \begin{matrix}{{{1000 \cdot T_{mcot}} + {{\left( {\left\lfloor \frac{T_{mcot}}{T_{j}} \right\rfloor - 1} \right) \cdot T_{js}}\mspace{14mu} u\mspace{20mu}\sec}},} & {{if}\mspace{14mu}\frac{T_{mcot}}{T_{j}}\mspace{20mu}{is}\mspace{14mu}{integer}} \\{{{1000 \cdot T_{mcot}} + {{\left\lfloor \frac{T_{mcot}}{T_{j}} \right\rfloor \cdot T_{js}}\mspace{14mu} u\mspace{20mu}\sec}},} & {otherwise}\end{matrix} \right. & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

The MCOT configuration method can be identically applied not only to DLtransmission but also to UL transmission.

3.2.4 LBT Method for Cooperative Multi-Point (CoMP) Transmission

Similar to LTE system of a legacy licensed band, CoMP (cooperativemulti-point) transmission of which a plurality of adjacent cells arecooperate can be applied to DL transmission in an unlicensed band aswell. The present invention proposes an LBT method that enables aplurality of TPs (transmission points) to perform DL transmission (e.g.,transmission of CRS, CSI-RS, DMRS, PDCCH, PDSCH, etc.) at the same timein the aspect of a random UE.

3.2.4.1 First LBT Method for CoMP Transmission

A method of supporting simultaneous transmission between TPs by aligningLBT parameters (e.g., CWS, backoff counter, backoff slot time boundary,etc.) between TPs is proposed.

For example, a CWS is configured by inter-TP signaling (or a rulepredetermined using an SFN (subframe number) and/or a cell ID) and abackoff counter can be configured according to a rule predeterminedusing an SFN and/or a cell ID. In addition, although a starting value ofa backoff counter is the same, it may be able to configure a backoffcounter value to be periodically (or dynamically) synchronized betweenTPs in preparation of a case that a backoff counter value is differentlydecreased according to a channel status between TPs. And, since slottime boundaries at which backoff is performed are not synchronized dueto a defer period or the like, it may be able to configure a slot timeboundary to be periodically (or dynamically or by a rule predeterminedbetween TPs) synchronized between TPs.

3.2.4.2 Second LBT Method for CoMP Transmission

When a specific TP performs random backoff-based LBT only among aplurality of TPs, if the remaining TPs determine that a channel is idleduring X us (e.g., X=34 us) immediately before the specific TPperforming the random backoff-based LBT transmits a signal, the presentinvention proposes a method that a plurality of the TPs performsimultaneous transmission.

For example, if a backoff counter value of a TP performing randombackoff-based LBT becomes 1, corresponding information can be forwardedvia signaling between TPs. If it is determined as a channel is idleduring time as much as a defer period+one backoff slot time from thistiming, all TP may attempt to perform simultaneous transmission. In thiscase, the TP performing random backoff-based LBT can be changed wheneverthe LBT ends (by a determined rule or uniformly randomly) and the TP canbe configured to be maintained during minimum prescribed time (1second).

3.2.4.3 Third LBT Method for CoMP Transmission

The present invention proposes a method that one of a plurality of TPsis configured as a master TP and the remaining TPs are configured asslave TPs. According to the present invention, the master TP performsrandom backoff-based LBT only and the slave TPs do not perform the LBT.The present invention proposes a method that all TPs performsimultaneous transmission when the master TP successfully performs LBT.

In this case, when the master TP succeeds in performing LBT,corresponding information can be signaled to a plurality of the TPS viainter-TP signaling. In this case, the master TP can be changed wheneverthe LBT ends (by a determined rule or uniformly randomly) and the masterTP can be configured to be maintained during minimum prescribed time (1second).

3.2.4.4 Fourth LBT Method for CoMP Transmission

In the first to the third LBT methods for CoMP transmission, when a TPperforms LBT, the present invention proposes a method of configuring theTP to perform CCA in a restricted region of a frequency axis.

For example, it may be able to configure a TP to perform CCA via aspecific frequency band (e.g., center 6 RBs) according to a rulepredefined among a plurality of TPs and configure the TP not to transmita signal to the frequency band.

3.2.4.5 Fifth LBT Method for CoMP Transmission

In the first to fourth methods for CoMP transmission, when a TP performsLBT, the present invention proposes a method of configuring the TP toperform CCA after the TP cancels a signal transmitted by a specific TP.

For example, when TPs perform CCA, the TPs preferentially detect asignal predetermined among a plurality of TPs (determined via inter-TPsignaling). If the signal is detected, the TPs cancel the signal. If anenergy value of the remaining signal is greater than a specificthreshold, the TPs determine that a channel is busy. Otherwise, the TPscan determine that the channel is idle.

3.2.5 Method of Defining Maximum Channel Occupancy Time (MCOT)

In Rel-13 LAA system, MCOT is defined as maximum time during which aneNB is able to perform transmission by occupying a channel after the eNBsecures the channel. In this case, since Rel-13 LAA system considers DLtransmission only, a scheduler is matched with a transmission entity.Hence, it was able to simply define MCOT in the aspect of the eNB.However, in case of Rel-14 enhanced LAA system considering ULtransmission as well as DL transmission, it is necessary to newly defineMCOT.

FIG. 16 is a diagram illustrating a method of defining MCOT proposed bythe present invention.

In FIG. 16, assume that an eNB starts DL transmission at a subframeboundary, transmits a signal in 3 full subframes and 1 DwPTS, andreceives UL transmission scheduled by a UE in 4 contiguous subframes.The eNB additionally configures a TA offset to make UL reception timingof the UE precede a subframe boundary as many as k symbols (e.g., k=1, kcan be configured via physical layer signaling or higher layersignaling).

According to the proposal, it may allow a UE to perform transmission inMCOT obtained by an eNB after the eNB performs LBT. To this end, the UEcan perform LBT which is determined in advance or is configured bysignaling (e.g., it may attempt to perform transmission if a channel isidle for prescribed time without random backoff).

3.2.5.1 First Method of Defining MCOT

When MCOT is defined in the aspect of an eNB, the MCOT can be defined bya time period of absolute time (irrespective of whether or not a TAoffset is additionally configured) from the timing (includingtransmission timing of a reservation signal for occupying a channel) atwhich DL transmission starts by the eNB.

3.2.5.2 Second Method of Defining MCOT

When MCOT is defined in the aspect of a UE, the MCOT can be defined by atime period ranging from the timing at which DL reception of a UE starts(including time for which LBT defined in the MCOT obtained by the eNB isperformed) to the timing at which UL transmission ends. In this case,the MCOT may or may not include the time for which LBT defined in theMCOT obtained by the eNB is performed.

3.2.5.3 Third Method of Defining MCOT

Unlike the abovementioned second MCOT definition method, MCOT can bedefined in the aspect of a UE irrespective of an additionally configuredTA offset. In particular, compared to the second MCOT definition method,the MCOT can be defined by a time period to which time as much as a TAoffset is added from the timing at which UL transmission ends.

3.2.5.4 Fourth Method of Defining MCOT

When MCOT is defined in the aspect of a UE, the MCOT can be defined bytime including absolute time (e.g., 8 ms) from the timing at which DLreception of a UE starts.

A length of the remaining MCOT can be implicitly or explicitly (e.g.,via scheduling DCI or common PDCCH) indicated using the aforementionedMCOT definition method. In this case, the MCOT may correspond to maximumoccupancy time obtained by an eNB after LBT is performed.

For example, in FIG. 16, if a length of the remaining MCOT is indicatedby M at the timing of SF #4 (or previous timing), MCOT ending timing canbe differently interpreted according to the aforementioned MCOTdefinition method.

According to the first MCOT definition method, the MCOT ending timingmay correspond to a boundary of an M^(th) subframe appearing after theSF #4. According to the second MCOT definition method, the MCOT endingtiming may correspond to time appearing after the M number of subframesfrom the timing at which DL reception of UE starts. According to thethird MCOT definition method, the MCOT ending timing may correspond totime as much as the timing at which transmission of the M number of ULsubframes ends+TA offset. According to the fourth MCOT definitionmethod, the MCOT ending timing may correspond to timing appearing afteran M^(th) subframe boundary+propagation delay from the SF #4.

3.2.6 LBT for Transmitting Subframe Including UL Scheduling DCI withoutPDSCH

In LAA Scell, when an eNB intends to schedule a UE to which self-carrierscheduling is set, if the eNB does not have PDSCH to be transmitted, theeNB can transmit a DL subframe consisting of UL grants only withoutPDSCH (hereinafter, UL grant only SF). When the eNB performs LBT beforethe UL grant only SF is transmitted, the eNB can perform relatively fastLBT (e.g., LBT of channel access priority class 1, LBT startingtransmission when a channel is idle during prescribed time (at least 25us) only, etc.) By doing so, in case of performing self-scheduling, itmay be able to mitigate a penalty such that LBT is to be succeeded notonly by a UL transmission UE but also by a scheduling eNB.

However, if LBT (hereinafter, fast LBT) relatively faster than a DLsubframe including PDSCH is frequently performed, UL grant only SF canbe too frequently transmitted. Then, not only the DL subframe but also ascheduled UL subframe frequently occurs. As a result, a problem mayoccur in coexisting with a different operator LAA or a different systemin an unlicensed band. The present invention proposes a method forsolving the problem.

3.2.6.1 First UL Grant Method

When a specific eNB transmits a UL grant only SF using fast LBT, aminimum transmission period (e.g., T ms or K subframes) of the UL grantonly SF can be configured. For example, if an eNB transmits a UL grantonly SF after fast LBT is successfully performed in an SF #n, the eNBcan attempt to transmit UL grant only SF via fast LBT after an SF #n+k.

3.2.6.2 Second UL Grant Method

When a specific eNB transmits a UL grant only SF using fast LBT, aminimum transmission period of the UL grant only SF can be differentlyconfigured according to a traffic type of UL data corresponding to acorresponding UL grant. For example, a UL traffic type can be classifiedinto 4 categories and an eNB can identify a category to which UL trafficbelongs thereto to be transmitted by each UE via a BSR (buffer statusreport) received from each of UEs. In this case, it is able to configurea minimum transmission period of a UL grant only SF, which istransmitted using fast LBT, according to a category. (e.g., in case of acategory 1, T1 ms or K1 subframes, in case of a category 2, T2 ms or K2subframes, in case of a category 3, T3 ms or K3 subframes, and in caseof a category 4, T4 ms or K4 subframes). In particular, when an eNBtransmits a UL grant only SF after fast LBT is successfully performed inan SF #n, if the eNB identifies that UL traffic of a scheduled UEcorresponds to the category 1, the eNB may attempt to transmit a ULgrant only SF via fast LBT after an SF #n+K1 (or T1 ms).

The aforementioned method can be identically applied not only totransmission of a UL grant only SF using fast LBT but also to a generalUL channel or signal. For example, it may be able to define a minimumtransmission period of a PRACH (physical random access channel) to whichfast LBT is applied, PUCCH (without PUSCH), PUSCH with UCI, or SRSwithout PUSCH. In this case, the transmission period can beUE-specifically configured or can be configured in the aspect of an eNBscheduler. For example, when the transmission period is configured inthe aspect of the eNB scheduler, if there is a UE 1 and a UE 2associated with a certain eNB and at least one of the UE 1 and the UE 2transmits PRACH (or PUCCH (without PUSCH), PUSCH with UCI, or SRSwithout PUSCH) by applying the fast LBT at the timing of an SF #n, boththe UE 1 and the UE 2 can attempt to transmit the PRACH (or PUCCH(without PUSCH), PUSCH with UCI, or SRS without PUSCH) via the fast LBTafter an SF #n+k. In this case, a minimum transmission period can bedifferently configured according to a UL channel (via predetermineddynamic signaling or higher layer signaling).

Since it is able to include the examples for the proposed method as oneof implementation methods of the present invention, it is apparent thatthe examples are considered as a sort of proposed methods. Although theembodiments of the present invention can be independently implemented,the embodiments can also be implemented in a combined/aggregated form ofa part of embodiments. It may define a rule that an eNB/location serverinforms a UE of information on whether to apply the proposed methods(or, information on rules of the proposed methods) via a predefinedsignal (e.g., physical layer signal or higher layer signal).

4. Device Configuration

FIG. 17 is a diagram illustrating configurations of a UE and a basestation capable of being implemented by the embodiments proposed in thepresent invention. The UE and the base station shown in FIG. 17 operateto implement the embodiments of a method of transmitting and receivinguplink data and a modulation reference signal between the UE and thebase station.

A UE 1 may act as a transmission end on a UL and as a reception end on aDL. A base station (eNB) 100 may act as a reception end on a UL and as atransmission end on a DL.

That is, each of the UE and the base station may include a Transmitter(Tx) 10 or 110 and a Receiver (Rx) 20 or 120, for controllingtransmission and reception of information, data, and/or messages, and anantenna 30 or 130 for transmitting and receiving information, data,and/or messages.

Each of the UE and the base station may further include a processor 40or 140 for implementing the afore-described embodiments of the presentdisclosure and a memory 50 or 150 for temporarily or permanently storingoperations of the processor 40 or 140.

The UE receives first DL control information indicating whether a typeof scheduling uplink signal transmission for one or more subframescorresponds to scheduling of a first type or scheduling of a second typefrom the base station via the processor 40. If the first DL controlinformation indicates the scheduling of the first type, the UE can beconfigured to transmit an uplink signal in one or more subframes whichare configured on the basis of the reception timing of the first DLcontrol information. If the first DL control information indicates thescheduling of the second type, the UE can be configured to receivesecond DL control information indicating UL signal transmission for oneor more subframes from the base station and transmit the uplink signalin one or more subframes which are configured on the basis of thereception timing of the second DL control information.

The base station transmits first DL control information indicatingwhether a type of scheduling uplink signal transmission for one or moresubframes corresponds to scheduling of a first type or scheduling of asecond type to the UE via the processor 140. If the first DL controlinformation indicates the scheduling of the first type, the base stationcan be configured to receive an uplink signal in one or more subframeswhich are configured on the basis of the reception timing of the firstDL control information. If the first DL control information indicatesthe scheduling of the second type, the base station can be configured totransmit second DL control information indicating UL signal transmissionfor one or more subframes to the UE and receive the uplink signal in oneor more subframes which are configured on the basis of the receptiontiming of the second DL control information.

The Tx and Rx of the UE and the base station may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDM packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the base stationof FIG. 17 may further include a low-power Radio Frequency(RF)/Intermediate Frequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory 50or 150 and executed by the processor 40 or 140. The memory is located atthe interior or exterior of the processor and may transmit and receivedata to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention can be applied to variouswireless access systems including 3GPP (3rd Generation PartnershipProject) and 3GPP2 system. The embodiments of the present invention canbe applied not only to various wireless access systems but also to alltechnical fields to which the various wireless access systems areapplied. Further, the proposed method can also be applied to an mmWavecommunication system using ultrahigh frequency band.

What is claimed is:
 1. A method of receiving a downlink signal by a user equipment (UE) from a base station in a wireless communication system supporting an unlicensed band, the method comprising: performing, by the UE, a reception of a first physical downlink control channel (PDCCH) comprising uplink scheduling information, in a subframe#n of the unlicensed band, based on determination that (i) information indicating that a number of occupied symbols for the subframe#n of the unlicensed band is less than 14 is not received in a subframe#n−1 of the unlicensed band and (ii) the UE identifies that the occupied symbols for the subframe#n is less than 14 during the subframe#n, where n is an integer larger than
 1. 2. The method of claim 1, wherein the first PDCCH is received via a UE-specific search space.
 3. The method of claim 1, wherein the information is included in a common PDCCH received via a common search space.
 4. A user equipment (UE) receiving a downlink signal in a wireless communication system supporting an unlicensed band, the user equipment comprising: a receiver; and a processor configured to operate in a manner of being connected with the receiver, wherein the processor controls the receiver to receive a first physical downlink control channel (PDCCH) comprising uplink scheduling information, in a subframe#n of the unlicensed band, based on determination that (i) information indicating that a number of occupied symbols for the subframe#n of the unlicensed band is less than 14 is not received in a subframe#n−1 of the unlicensed band and (ii) the UE identifies that the occupied symbols for the subframe#n is less than 14 during the subframe#n, where n is an integer larger than
 1. 5. The UE of claim 4, wherein the first PDCCH is received via a UE-specific search space.
 6. The UE of claim 4, wherein the information is included in a common PDCCH received via a common search space.
 7. The method of claim 1, wherein the UE identifies that the occupied symbols for the subframe#n is less than 14 during the subframe#n, based on a second PDCCH received via a common search space in the subframe#n of the unlicensed band.
 8. The method of claim 1, wherein the subframe#n corresponds to an ending partial subframe that at least one last symbol is not occupied.
 9. The UE of claim 4, wherein the UE identifies that the occupied symbols for the subframe#n is less than 14 during the subframe#n, based on a second PDCCH received via a common search space in the subframe#n of the unlicensed band.
 10. The UE of claim 4, wherein the subframe#n corresponds to an ending partial subframe that at least one last symbol is not occupied. 